As for a metal oxide sol including a hydrophobic organic solvent as the dispersion medium, for example, known is a method for producing an organic solvent dispersed inorganic oxide sol in which inorganic oxide particles having a surface with a silicon atom to which a C3-12 primary alkoxy group is bonded are stably dispersed in an organic solvent such as methyl ethyl ketone (see Patent Document 1).
Furthermore, there has been disclosed a sol that includes an aqueous sol or an organic solvent-dispersed sol of anhydrous zinc antimonate as a core coated with a silicon-containing substance such as a silane coupling agent and a silylation agent and includes an amine or an oxycarboxylic acid (see Patent Document 2).
There has also been disclosed a stable sol that includes modified stannic oxide-zirconium oxide composite colloidal particles having a particle diameter of 4.5 to 60 nm and a method for producing the sol. The modified stannic oxide-zirconium oxide composite colloidal particles include, as cores, composite colloidal particles of stannic oxide-zirconium oxide having a structure in which colloidal particles of stannic oxide are bonded with colloidal particles of zirconium oxide at a ZrO2/SnO2 ratio of 0.02 to 1.0 based on weight of these oxides, having a particle diameter of 4 to 50 nm, and having a surface coated with tungsten oxide-stannic oxide-silicon dioxide composite colloidal particles that have a WO3/SnO2 mass ratio of 0.1 to 100, a SiO2/SnO2 mass ratio of 0.1 to 100, and a particle diameter of 2 to 7 nm. The sol has a total metal oxide content of 2 to 50% by mass (see Patent Document 3).